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Biomedical subjects

I A Anderson

Publications and source records attributed to I A Anderson.

10 recordsLinked to original sources
PubMed2006

Accuracy of a computer-assisted navigation system for total knee replacement.

The object of this study was to develop a method to assess the accuracy of an image-free total knee replacement navigation system in legs with normal or abnormal mechanical axes. A phantom leg was constructed with simulated hip and knee joints and provided a means to locate the centre of the ankle joint. Additional joints located at the midshaft of the tibia and femur allowed deformation in the flexion/extension, varus/valgus and rotational planes. Using a digital caliper unit to measure the coordinates precisely, a software program was developed to convert these local coordinates into a determination of actual leg alignment. At specific points in the procedure, information was compared between the digital caliper measurements and the image-free navigation system. Repeated serial measurements were undertaken. In the setting of normal alignment the mean error of the system was within 0.5 degrees . In the setting of abnormal plane alignment in both the femur and the tibia, the error was within 1 degrees . This is the first study designed to assess the accuracy of a clinically-validated navigation system. It demonstrates in vitro accuracy of the image-free navigation system in both normal and abnormal leg alignment settings.

Arthroplasty, Replacement, Knee↗
PubMed2005

A cerebral palsy assessment tool using anatomically based geometries and free-form deformation.

A geometrical analysis tool for investigating muscle length change in cerebral palsy (CP) patients is presented. A subset of anatomically based geometries from the International Union of Physiological Sciences (IUPS) Physiome Project is used, which is derived from the visible human (VH) data set with muscle attachment information, and customised using volume-preserving free-form deformation (FFD), the 'host-mesh' technique. The model's intended use is to provide pre- and post-surgery assessment for muscle lengthening, a surgery performed to help slacken tight muscles and improve gait. The model is illustrated using healthy patient data from motion capture as a validation followed by three CP case studies to highlight its use. The methodology is presented in three stages, (1) a FFD of the complete lower limb, (2) a focused geometric study on the semimembranosus (SM) and gastrocnemius (GT) muscles, and (3) an improved hybrid mechanics-FFD approach as an improvement for future analysis, with differentiation between muscle and tendon lengthening, and contact detection between sliding muscles. Finally, the issues, limitations, in particular with the marker system, and model improvements are discussed.

Cerebral Palsy↗
PubMed2005

Stress analysis of hemispherical ceramic hip prosthesis bearings.

We present design criteria and test data for ceramic hemispherical 'resurfacing' prosthesis bearings that are attached by placement on the conical trunnion of the prosthesis stem. These large diameter bearings will be subjected to higher torques than conventional 28 mm bearings. Prototypes were fabricated and tested. The pattern of failure and subsequent analysis suggests that fracture initiated on the surface of the bore and that this was preceded by the development of large circumferential hoop stresses. Widening the bore will improve stability under torque loads but this may be at the expense of bearing strength. A finite element analysis has shown that the optimum taper bore to bearing diameter ratio is 0.43 and that designs with large taper bore to bearing diameter ratios (over 0.6) should be avoided due to the development of excessively high hoop stresses on the inner bore surface. High meridional tensile stresses can appear where the internal roof surface joins the conical bore surface as the load is removed. A smooth radius between the conical bore and the roof will help to overcome this. Further improvements include a thinner roof that is smoothly arched internally. Thus, the design of the component can be optimised, making it less susceptible to fracture without compromising the stability of the ceramic head on its trunnion.

Arthroplasty, Replacement, Hip↗
PubMed2005

Anatomically based modelling of the human skull and jaw.

We present here an anatomically based model of the human masticatory system that provides a framework for simulating the complex chewing process. The initial motivation for creating this model was the desire to have a computational model of the human jaw that can be used to simulate the action of simple bites, and to calculate the stresses and forces on the teeth that are involved. The model created also provides a platform that can be used to investigate other features of the masticatory system. To construct this global model, individual models of the bones of the skull and jaw were created from generic data sets. Geometric models of the muscles of mastication were also created and attached to the appropriate bones. To complete this initial model, representations of the crowns of the teeth were created and a basic model of the temporomandibular joint (TMJ) was included. The finite element method was used to solve for the stresses and strains created by the loading conditions during a clenching simulation involving the mandible bone. The model presented here is also discussed in relation to a model of the entire musculo-skeletal system being developed as part of the Physiome Project.

Computer Simulation↗
PubMed2000

How do changes to plate thickness, length, and face-connectivity affect femoral cancellous bone's density and surface area? An investigation using regular cellular models.

Models of regular cellular-solids representing femoral head 'medial group' bone were used to (1) compare thickness data for plate-like and beam-like structures at realistic surface areas and densities; (2) test the validity of a standard formula for trabecular thickness (Tb.Th); and (3) study how systematic changes in cancellous bone thicknesses, spacing, and face-connectivity affect relative density and surface area. Models of different face-connectivities, produced by plate removal from the unit cell, were fitted to bone density and surface area data. The medial group bone was anisotropic: the supero-inferior (SI) direction was the principal direction for bone plate alignment and the plane normal to this had the largest number of bone/void intersections per unit line length (P(I)). A comparison of boundary perimeter per unit area data, in planes normal to SI, with surface area data placed the medial group bone between prismatic structures in which walls are parallel to one principal direction and isotropic structures. Selective removal of plates from a closed-cell model produced a similar result. For the same relative density and surface-area, plate-like models had significantly thinner cross-sections than beam-like models. The formula for Tb.Th produced overestimates of model plate thickness by up to 20% at realistic femoral cancellous densities. Trends in data on surface area to volume ratio and density observed on sampled medial group bone could be simulated by plate thickness changes on models of intermediate face-connectivity (approximately 1.5) or by plate removal from models with relatively thick and short (low aspect-ratio) plates. The latter mechanism is unrealistic for it resulted in beam-like structures at low 'medial group' densities, an architecture unlike the predominantly plate-like bone in the sample.

Aged↗
PubMed2000

The processing and characterization of animal-derived bone to yield materials with biomedical applications. Part III: material and mechanical properties of fresh and processed bovine cancellous bone.

Conversion of bovine cancellous bone to a useful biomedical xenograft material involves several processing steps which include boiling, defatting and deproteination (i.e. bleaching). This study has shown how these processes can influence cancellous bone modulus and strength. It was found that prolonged boiling in water for six hours followed by NaOCl bleaching had a deleterious effect on the overall strength of the bovine bone. In contrast, bone samples subjected to only moderate boiling (1.5 hours) exhibited a 22% stiffness increase due mainly to the effects of drying. The same stiffened samples, when subjected to the bleaching procedure, retained some strength with only a small reduction in moduli values. It can be concluded that careful control of defatting and bleaching procedures on bovine bone is able to give a strong, albeit, brittle material with preservation of the original bone architecture. The bone xenograft materials are worthy of further investigation in in vivo clinical trials to assess their performance in contact with biological fluids.

Journal Article↗
PubMed1991

Haematology and histopathology of seven-week-old broilers after early food restriction.

The haematology and histopathology of seven-week-old broilers were examined after periods of early food restriction, for six, 10 or 14 days from six days old. After several weeks on an ad libitum diet the birds failed to compensate for the weight lost during early food restriction. Immediately after the periods of food restriction, the birds demonstrated significantly increased heterophil/lymphocyte ratios, reduced eosinophils and slightly raised basophil counts. At seven weeks old, a significant reduction was seen in red and white blood cells and thrombocyte numbers together with significant increases in mean cell haemoglobin and mean cell volume. The haematological profile demonstrated a macrocytic normochromic anaemia caused possibly by a folic acid deficiency as a result of the food restriction. Histopathological lesions were seen in the heart, lungs and liver from birds on all diets but there were more lesions the longer the food had been restricted. Lung disease was more marked where there was inadequate ventilation. Cartilaginous and osseous lung nodules were significantly fewer after food restriction. It was postulated that the increase in pathological lesions in the food-restricted birds may be associated with a stress response.

Animals↗
PubMed1986

The gastrocnemius tendon of domestic fowl: histological findings in different strains.

Vascular and histological studies were performed on normal gastrocnemius tendons from male birds considered susceptible (broiler breeding) and insusceptible (laying strain) to noninfectious tendon rupture. Structural differences between strains were noted at the site where rupture usually occurs. This site contains a hypovascular region which develops at an earlier age in broiler type fowls. Histological sections revealed that vessel occlusion had occurred in birds with hypovascular tendon segments. Chondrocytes and chondroid cells adjacent to occluded vessels accumulated lipid and died. This finding was particularly apparent in broiler fowls where cartilaginous plaques were larger and thicker than in laying strain fowls. The presence of occluded vessels, cartilage death and chondroid infiltration of collagen bundles in broiler type fowls are interpreted as structural changes which may predispose to noninfectious tendon rupture. Indeed they may also predispose to tendon lesions associated with pathogens.

Animals↗